1. Field of the Invention
The present invention relates to a gas laser device, and more particularly to a discharge circuit for a gas laser device.
2. Description of the Present Art
A discharge circuit for a gas laser device, briefly described, usually comprises a positive electrode, connected to a source of DC power, opposing a plurality of negative electrodes, with a stabilized resistance connected in series with each negative electrode respectively. In a discharge circuit of this configuration there are no particular problems during continuous discharge. However, in order to carry out a pulse discharge, when a source of pulsed power is used in place of the previously mentioned source of DC power, the discharge is intermittent, so that the onset of the discharge current is delayed, causing the build up time to be extremely long. Accordingly, in the case where a rectangular waveform, for example, is used as an electric power pulse wave, the onset of the discharge current is considerably delayed and the wave form breaks down.
In order to reduce the delay in the onset of the above mentioned discharge current, conventionally, an extremely weak discharge of current at a level where laser generation does not occur, known as a simmer discharge, is always maintained between the positive and negative electrodes. The pulse voltage is accumulated in this status and the pulse discharge is carried out in the usual manner. In a circuit which performs this type of pulse discharge, a positive electrode is connected to both the simmer and pulse power sources and a plurality of negative electrodes are positioned in opposition. One of a plurality of stabilized resistances for simmer use is connected in series to each of the negative electrodes, and one of a plurality of stabilized resistances for pulse use, connected to the pulse power source, is connected in parallel to each. The stabilized resistance for simmer use is put at a value of several times that of the abovementioned stabilized resistance for pulse use, to make the simmer current sufficiently smaller than the pulse current.
In a conventional circuit with a configuration such as outlined above, the simmer power and pulse power, when OFF, have a rather high internal impedance. The pulse power is maintained in OFF status and the simmer power is turned ON first. The voltage of the simmer power increases, and when it exceeds the initial discharge voltage between the positive and negative electrodes, discharge commences between the positive electrode and one suitable negative electrode. when this discharge commences, current flows between the positive electrode and that one suitable negative electrode, and the voltage between the positive electrode and that one suitable negative electrode becomes the discharge support voltage, which has dropped from the initial value by the product of the stabilized simmer resistance and the amperage. This discharge support voltage is considerably lower than the initial discharge voltage.
In this manner, the current which flows from the positive electrode and that one suitable negative electrode passes through the stabilized simmer resistance connected to that one negative electrode. It then passes through the parallel circuits of the stabilized pulse resistances and the stabilized simmer resistances connected to the other negative electrodes from the parallel stabilized pulse resistances and returns to the simmer power source. In this case, the voltage between the positive electrode and those other negative electrodes is just slightly higher than the voltage between the positive electrode and that one negative electrode, and is considerably lower than the initial discharge voltage. Accordingly, in order that discharge will take place between the positive electrode and those other negative electrodes, a large voltage is necessary, with the result that a large current is necessary.
Because of this, the voltage of the simmer power source must be extremely high in order to cause a discharge between the positive electrode and those other negative electrodes, after the discharge takes place between the positive electrode and that one negative electrode. Specifically, a high voltage and large amperage is required at the simmer power source, and a large current flows between the positive electrode and that one negative electrode during the interval up to the commencement of discharge between the positive electrode and those other negative electrodes. Accordingly, a large amperage is necessary to obtain a discharge between the positive electrode and all the negative electrodes.
However, in actual fact, because an extremely small amperage at a level where laser generation does not occur flows at the simmer discharge, the simmer discharge is produced between a number of the negative electrodes and only one portion of the positive electrode. Accordingly, when the pulse voltage is applied, it is applied simultaneously between the electrodes in which the simmer discharge is taking place as well as the electrodes in which the simmer discharge is not taking place. In the case where the pulse voltage is applied between the electrodes in which the simmer discharge is taking place, the build-up time of the discharge current is small so that the variation between each pulse is also small. However, in the electrodes in which the simmer discharge is not taking place, the build-up time of the discharge current is large so that the variation between each pulse is also large.
Accordingly, in a conventional circuit in which the simmer discharge is produced between the positive electrode and one part of the negative electrodes only, not between the positive electrode and all the negative electrodes, the pulse build-up time becomes large for all pulse discharge currents which are the accumulated discharge current pulses between the positive electrode and each negative electrode, respective to the waveform of the applied pulse voltage. Furthermore, the pulse waveform is broken down. With a pulse waveform in which the discharge current is broken down in this way, the pulse output waveform of the laser beam is also broken down, and, in addition, there is an obstacle in increasing the pulse frequency.